1. Field of the Invention
The present invention relates to digital video, and, in particular, to memory devices for storing and processing video pixel data.
2. Description of the Related Art
In digital video systems, images are represented by arrays of pixels (i.e., picture elements). Each pixel is typically represented by three values, e.g., red R, green G, and blue B values in the RGB system or one luminance value Y and two chrominance values U and V in the Phase Alternating Line (PAL) or YUV system.
As digital video images are generated by a video capture source (e.g., a CCD-based video camera), pixel data may be transmitted from the video capture source in a packed format. In a packed format, all the data for a given pixel are transmitted before any data for another pixel are transmitted. As a result, in packed format, the pixel components (e.g., RGB or YUV) are interleaved in the pixel data stream transmitted by the video capture source.
Graphic displays in conventional digital video systems receive and display video data in a packed format. Thus, when video images generated by a video capture source are displayed in real time on a graphic display, the video data are preferably transmitted to the graphics frame buffer of the graphic display in a packed format.
As an alternative to immediate display, video data may be stored in memory for future display. To store video data efficiently (i.e., utilizing minimal storage capacity), conventional digital video systems contain a data compressor that compresses the video data using compression techniques. Many conventional compression techniques are based on compressing the video data by processing the different pixel components separately. For example, a YUV-data compressor may run-length encode the Y data independently of a run-length encoding of the U data and a run-length encoding of the V data. Such a compressor preferably receives video data in a planar format, in which the Y, U, and V data for multiple pixels are separated and grouped together in three distinct data streams of only Y, only U, and only V data.
"Packed" memory devices exist for receiving video data from a video capture source in a packed format and for transmitting video data in a packed format for display on a graphic display. In addition, "planar" memory devices exist for receiving video data from a video capture source in a packed format and for transmitting video data in a planar format for compression by a video compressor. However, known packed memory devices cannot transmit planar-format data and known planar memory devices cannot transmit packed-format data.
It is desirable to build a digital video system that has the flexibility of either displaying video data immediately on a graphic display or compressing video data for storage with a data compressor. Since known packed memory devices transmit only packed data and since known planar memory devices transmit only planar data, such a flexible digital video system has conventionally contained both types of memory devices. Such systems make inefficient use of memory resources, since each of the two memory devices has its own independent memory allocation.
It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the prior art and to provide a single memory device that transmits either packed-format data for display or planar-format data for compression, in a flexible digital video system.
It is a further object of this invention to improve the memory usage efficiency of a digital video system that can either display video images in real time as they are generated or compress video data for storage for future display.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.